Process for stabilization of diolefin-containing hydrocarbons

ABSTRACT

A PROCESS FOR STABILIZING DIOLEFINS IN CRACKED HYDROCARBON OILS BY REACTION WITH HYDROGEN SULFIDE IN THE PRESENCE OF HYDROGEN TO PREVENT OR REDUCE POLYMERIZATION AND GUM FORMATION ON SUBSEQUENT HEATING. IN ONE EMBODIMENT THE PROCESS IS USED IN CONNECTION WITH CONVENTIONAL HYDROGENATION/HYDROSULFURIZATION TO STABILIZE DIOLEFIN-CONTAINING CRACKED OILS BY CONVERSION, AT LEAST IN PART, OF DIOLEFINS TO ORGANIC SULFUR COMPOUNDS FOLLOWED BY SUBSEQUENT HYDROGENATION AND DESULFURIZATION.   D R A W I N G

July 27, 1971 c. T. ADAMS ETAL 3,595,780 I PROCESS FOR STABILIZATION OF DIOLEFIN-CONTAINING HYDROCARBONS Filed May 1, 1969 SEPARATION ZONE SECOND REACTION ZONE INVENTORS:

CHARLES T. ADAMS RICHARD IE. FRUIT THETR ATTORNEY FEED United States Patent O PROCESS FOR STABILIZATION F DIOLEFIN- CONTAINING HYDROCARBONS Charles '11. Adams, Houston, and Richard E. Fruit, La

Porte, Tex assignors to Shell Oil Company, New York, N.Y.

Filed May I, 1969, Ser. No. 820,759

Int. Cl. Cg 23/02 U.S. Cl. 208-216 10 Claims ABSTRACT OF THE DISCLOSURE A process for stabilizing diolefins in cracked hydrocarbon oils by reaction with hydrogen sulfide in the presence of hydrogen to prevent or reduce polymerization and gum formation on subsequent heating. In one embodiment the process is used in connection with conventional hydrogenation/hydrosulfurization to stabilize diolefin-containing cracked oils by conversion, at least in part, of diolefins to organic sulfur compounds followed by subsequent hydrogenation and desulfurization.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a process for stabilizing diolefin-containing cracked hydrocarbon oils.

Discussion of the prior art When hydrocarbon oils are subjected to severe ther mal cracking or pyrolysis for the production of light olefins (ethylene, propylene, butylenes, etc.), the heavier product fractions, i.e., gasoline and higher boiling range materials, are generally high in aromatics and olefins, including a substantial concentration of diolefins. The unstable diolefins as well as vinyl aromatics and acetylenic compounds which may be present tend to polymerize on heating, making further processing, even distillation, difficult. Moreover, these components lead to gum formation during storage. Since aromatics, and olefins to a lesser extent, are desirable high octane number components in gasoline, it has been the practice in the past to selectively hydrogenate diolefin-containing oils to partially saturate the diolefins thereby increasing their stability and suitability for further use. Various processes for selective hydrogenation have been proposed. The following are illustrative: Bryant, U.S. 3,309,307, March 1967; Laughout et al., U.S. 3,234,298, February 1968; and Eng et al., U.S. 3,394,199, July 1968. In all these proposals diolefins are selectively hydrogenated with little or no hydrogenation of monoolefins or aromatics. Such selective hydrogenation is appropriate and suitable for stabilization of pyrolysis by-products when the pyrolysis feed stock is relatively low boiling naphtha which contains only a small amount of heteroatomic impurities such as organic sulfur and nitrogen compounds. However, mild selective hydrogenation does not generally reduce organic sulfur and nitrogen compounds to any appreciable extent and this treatment alone is insufficient to stabilize heavier fractions. This becomes an increasingly difficult problem as the pyrolysis feed stock boiling range is increased. For example, when using a gas oil (as opposed to naphtha) pyrolysis feed, which in general is significantly higher in sulfur content, the heavy pyrolysis product usually must be further hydrofined a reaction requiring more severe conditions, particularly higher temperatures. In this case an initial treatment for the purpose of stabilizing the diolefin-containing oil to prevent polymerization with concomitant coking in the subsequent hydrofining preheaters and catalyst bed is required.

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We have now discovered that diolefin stabilization can be effectively accomplished by catalytic reaction of diolefin-containing feed with a sulfur compound in the presence of hydrogen. This treatment may be accompanied by hydrogenation but coincident hydrogenation is not essential to the effectiveness of the present process.

SUMMARY OF THE INVENTION The invention is a process for catalytic conversion of diolefin-containing hydrocarbon oils by reaction with a sulfur compound whereby diolefins are at least partially converted to organic sulfur compounds in the presence of hydrogen. In one embodiment, the invention is a multistage process for the catalytic conversion of diolefin-containing hydrocarbon oils wherein diolefins are at least partially converted to sulfur compounds in a first reaction stage and thereafter the oil is contacted with a hydrogenation catalyst in the presence of hydrogen at elevated temperature and pressure to reduce the concentration of organic sulfur and nitrogen compounds.

Hydrocarbon oils suitable for treating according to the process of the invention include any diolefin-containing normally liquid oils, as for example, those obtained from the pyrolysis of heavy naphtha or gas oil petroleum fractions. Thus, the feed stock can include fractions ranging from butane to pitch boiling above 800 F. In general, however, it is preferred that the feed consist principally of gasoline and gas oil boiling range materials (about to 800 F. boiling range).

Typically, hydrocarbon stocks as produced by pyrolysis have diolefin contents, as measured by the maleic anhydride condensation values (MAV), of 50 or above. It is generaly sufficient to achieve adequate stabilization by reducing diolefin content to a MAV value of about 25 or below.

The process is carried out by reacting diolefin-containing oil with a sulfur compound in the presence of hydrogen and a catalyst.

While any sulfur compound capable of reacting with diolefins may, in principle, be used, it is expedient and preferred to use hydrogen sulfide (H 8). Hydrogen sulfide is readily available, relatively inexpensive, and accomplishes the objectives of the invention.

When hydrogen sulfide is used, the concentration should be at least about 0.5% by volume basis hydrogen, and preferably above about 1.0% by volume. Concentrations above about 5.0% may be used but generally are not required. It is especially preferred that the concentration be about l.5%-3.0% by volume.

Reaction temperature should not be above about 350 F. and preferably not above about 300 F. Temperatures of about 275 F. are particularly effective although temperatures as low as about 200 F. may be employed, as shown in Example II below. The unstable nature of the diolefins requires that temperature be minimized to prevent rapid polymerization which leads to coking. Hydrogen pressure should be in the range of between 400 to 2000 psi. and preferably in the range of about 600 to 1200 psi.

Catalysts which are suitable for the reaction of diolefins include transition metal sulfides comprising a hydrogenative metal component selected from the group consisting of the sulfides of cobalt, nickel, molybdenum, tungsten and mixtures thereof, preferably supported on a relatively non-acidic solid support, i.e., a support having little cracking activity. Supports with high surface area are preferred. Particularly suitable catalysts are sulfided nickel or sulfided nickel and molybdenum supported on alumina. Such catalysts, which are well known in the art as hydrogenation catalysts, have been found to be especially effective in the process of the invention. The catalyst may be produced by various means known to the art, such as, for example, impregnating the metal onan alumina support or incorporating the metal into an alumina hydrogel followed by drying and calcining. In most conventional preparation techniques the metal component will be initially present, after calcination, as the metal oxide. For the purpose of the present invention the catalyst is converted to the sulfide form. This, as it is well known, is easily accomplished by contacting the catalyst with a suitable sulfur compound, as for example, hydrogen sulfide.

When a metal sulfide hydrogenation catalyst is used, some hydrogenation of the diolefin feed may occur. This is often desirable and aids in the removal of sulfur and nitrogen compounds. However, it has been found that in many cases hydrogenation activity of the catalyst used is rapidly lost. Surprisingly, however, the objective of the invention, i.e., the diolefin reduction and stabilization, does not depend upon hydrogenation and suitable stabilization is obtained with or without concurrent hydrogenation.

One important embodiment of the invention is a multistage process wherein diolefin-containing liquid hydrocarbon feed is first reacted with sulfur for stabilization by partial conversion of diolefins to organic sulfur compounds followed by hydrogenation at more severe conditions to remove or reduce organic sulfur and nitrogen compounds including those produced in the first reaction. This combined process facilitates the conversion of unstable diolefin-containing pyrolysis liquid products to stable products suitable for storage of further refining.

DESCRIPTION OF THE DRAWING The figure is a schematic representation of one embodiment of the invention. Diolefin-containing feed, such as a gasoline and gas oil boiling range pyrolysis liquid product, enters the process via line where it is mixed with fresh makeup-hydrogen from line 11 and/or hydrogen sulfide from line 12, and recycle hydrogen plus hydrogen sulfide via line 23. The mixture enters the first reaction zone 3 via common line 13.

The first reaction zone serves primarily to convert diolefins to organic sulfur compounds and by other unknown means to render the feed sufficiently stable to allow further heating and/or storage without appreciable polymerization or gum formation. This reaction zone contains a supported metal sulfide catalyst and is operated below about 350 F. and preferably below about 300 F., at a pressure between about 600 to about 2000 p.s.i.g.

The stabilized eflluent from the first reaction zone, richer in organic sulfur compounds than the feed, passes via line 15 to heater 5, and then to hydrogenation zone 7 where olefins are substantially saturated and organic nitrogen and sulfur compounds are, at least in part, converted to ammonia and hydrogen sulfide, respectively.

For the hydrogenation reaction any conventional hydrogenation catalyst or mixture thereof is suitable. For example, oxides or sulfides of metals of Groups VI and VIII of the Periodic Table of Elements can be used. These catalytic metals or compounds are conventionally supported on a suitable refractory oxide support. Examples of suitable support include oxides of aluminum, magnesium, zirconium, etc. It is preferred that the sup port have no substantial cracking activity. Alumina is preferred. Particularly suitable hydrogenation catalysts are sulfided nickel/ tungsten, nickel/molybdenum or cobalt molybdenum supported on alumina. Operating conditions will depend upon the nature of the feed, the amount and desired degree of removal of olefins, organic sulfur and nitrogen and other factors known in the art.

Suitable conditions will generally be in the range of 400600 F. and 600-2000 p.s.i.g. pressure. In a flow reaction system, space velocity will be in the range of about 0.1 to 5 LHSV (volume of feed/volume of catalyst/ hour). In most cases hydrogen uptake in this reaction zone will be about 2004500 s.c.f. Hz/bbl. feed. The effluent from reaction 7 is removed via line 17 and may be treated in various ways as will be apparent to those skilled in the art. The effluent may be distilled into fractions prior to gas separation. For the purposes of the invention, the efliuent passes to a gas separation zone 9 (for example, a flash zone) where the gas is removed. Liquid efiiuent having been substantially degassed, passes via line 18 for further treatment, use or storage.

The gas, containing principally hydrogen with smaller amounts of hydrocarbon gases, hydrogen sulfide and am monia, is removed via line 19. A portion of this gas is recycled via line 23 to the first reaction zone to supply the required hydrogen and hydrogen sulfide. The composition of the gas entering the first reaction zone 3 is controlled by regulation of the amount of recycle gas from line 23, hydrogen make-up from via line 11 and hydrogen sulfide-containing gas via line 12.

The following examples further illustrate the invention.

EXAMPLE I A gasoline/gas oil boiling pyrolysis liquid feed was treated in a small flow reactor. The feed had a density of 0.954 gm./cc. at 60 R, an organic sulfur content of about 0.3% w. and a MAV value of about 50. Comparison runs were made at 275 F., 1000 p.s.i.g., 3.5 H /oil (mole) and 1.0 LHSV with and without hydrogen sulfide addition to the feed hydrogen. The results of these runs are summarized in Table 1. The MAV value are average values obtained from daily analytical results.

The catalyst used was a sulfided nickel/molybdenum/ alumina hydrotreating catalyst. As can be seen, hydrogenation activity was lost rapidly as evidenced by the H consumption which dropped to zero after about 300 hours of operation.

With the addition of 1.5% v. H S (basis hydrogen), MAV reduction was markedly improved over the comparison run without H 8 addition.

When 1.5% v. H 3 was added to the run started without H 8 addition (at 520 hours), the product MAV dropped and equilibrated to the level obtained with H S addition throughout. The product produced during periods of H 8 addition contained about 0.7% W. sulfur as compared to 0.3% w. for the feed indicating at least partial reaction of diolefin With H S.

TABLE 1 {Conditions: 275 F.; 1,000 p.s.i.g.; 3.5 Hz/oil (mole) 1.0 LHSV] MAV of product 1 1.5 percent volume HzS added to H2 at 520 hours run time.

EXAMPLE II This example illustrates the effect of H 8 addition during the combined stabilization-hydrogenation of a pyrolysis gas-oil/gasoline blend.

The feed had an API gravity of 18.1 at 60 F. and a MAV value of 92.

This feed was processed in a pilot plant consisting of five reactors in series. The fresh feed rate was 1500 cc./hr. together with 199 cc./hr. recycle of total liquid product.

The catalyst used was a sulfided nickel/molybdenum on alumina hydrotreating catalyst as in Example I. The reactor catalyst loading ratio was 1:1:1: 1.5 1.5 in the five reactors, respectively. Pressure was p.s.i.g. with 36 s.c.f./hr. of hydrogen gas provided to the first reactor (fresh plus recycle gas).

Temperature progressively increased in the reactors as shown in Table 2. Hydrogen sulfide was added to the gas to provide about 1.5% mole H S (basis gas) to the first reactor.

The product MAV from the third reactor was 18 and essentially zero after the fifth reactor, which indicated efficient removal of diolefins.

The organic sulfur content of the effluent of each reactor, together with reactor inlet temperature, are shown in Table 2.

TABLE 2 Percent weight Organic sulfur content of effluent 1 1 Basis fresh teed, excluding recycle.

As can be seen, the feed, at temperatures below 462 F., reacted with the added H 8. This reaction provided saturation of the diolefins and helped stabilize the feed for hydrogenation at the higher temperature.

No pressure drop increase in the reactor system oc' curred during the more than 100 days of operation and the catalyst was =fluid on termination of the run. When no sulfur was added in previous similar pilot plant runs the catalyst was cemented together with coke and significant increase in reactor pressure drop occurred. This example thus demonstrates a preferred embodiment of the present invention when the sulfur reaction and hydrogenation reactions are conducted sequentially.

We claim as our invention:

1. A process for stabilization of a diolefin-containing hydrocarbon fraction whereby diolefins are at least partially converted to organic sulfur compounds which comprises reacting said fraction in the presence of hydrogen with a sulfur compound and a catalyst comprising a hydrogenative metal component selected from the group consisting of the sulfides of cobalt, nickel, molybdenum, tungsten and mixtures thereof supported on a relatively nonacidic inorganic refractory oxide at a temperature from about 200 F. to 350 F.

2. The process of claim 1 wherein the sulfur compound is hydrogen sulfide.

3. The process of claim 2 wherein the contacting is carried out under a pressure in the range of between about 600 to 2000 p.s.i.g.

4. The process of claim 1 wherein the hydrocarbon fraction is a cracked petroleum fraction boiling at least partially in the gas-oil boiling range.

'5. The process of claim 4 wherein the petroleum fraction has an initial maleic anhydride condensation value of at least about 50 and the fraction is stabilized by reducing diolefin content to a maleic anhydride condensation value below about 25.

6. The process of claim 2 wherein the refractory oxide support is alumina.

7. The process of claim 2 wherein the hydrogen sulfide concentration is between about 1.5% to 3.0% by volume basis hydrogen.

8. A process for stabilization of a diolefin-containing cracked petroleum fraction boiling at least partially in the gas-oil boiling range and containing organic sulfur compounds whereby diolefins are at least partially converted to organic sulfur compounds which comprises reacting said fraction in the presence of hydrogen with a sulfur compound and a catalyst comprising a hydrogenative metal component selected from the group consisting of the sulfides of cobalt, nickel, molybdenum, tungsten and mixtures thereof supported on a relatively non-acidic inorganic refractory oxide at a temperature from about 200 -F. to 350 F. and a pressure between about 600 psi. and 2000 p.s.i. wherein the contacted petroleum fraction is increased in organic sulfur compound content, followed by contacting the fraction in the presence of hydrogen with a hydrofining catalyst at a temperature above about 400 F. and a pressure above about 600 p.s.i.g. to reduce the organic sulfur compound content to below the level of that in the original petroleum fraction.

9. The process of claim 8 wherein the sulfur compound is hydrogen-sulfide.

10. The process of claim 8 wherein the hydrogen sulfide is present in a concentration of between about 1.5 to 3.0% by volume basis hydrogen.

References Cited UNITED STATES PATENTS 2,620,362 12/1952 Stiles 208-213 2,914,470 11/1959 Johnson et al. 208-264 3,050,458 8/1962 Vant Spijker et al. 208213 3,239,449 3/ 1966 Graven et .al 208-210 3,309,307 3/1967 Bryant, Jr. 208216 DELBERT E. GANTZ, Primary Examiner G. J. CRASANAKIS, Assistant Examiner U.S. Cl. X.R. 208*211, 217 

